Capacitive sensor device

ABSTRACT

A capacitive sensor includes a metal radiator disposed at an extreme end of a sensor assembly. A coaxial electrode is electrically interconnected to the metal radiator. The coaxial electrode has a center conductor, a dielectric around the center conductor, and an outer conductor, the center conductor being in electrical continuity with the metal radiator. An insulator configured to fit adjacent the metal radiator is configured to electrically and thermally isolate the metal radiator from selected electrical and thermal properties in an environment wherein the capacitive sensor probe is disposed. A connector is disposed distal from the metal radiator on the coaxial electrode, a portion of the connector being in electrical continuity with the metal radiator.

TECHNICAL FIELD

This specification relates to sensors, and in particular a capacitivesensor for use with various control systems.

BACKGROUND

Control systems are known, for controlling operation of energy or heatsources, such as in controlled cooking systems. In some known systems,such as deep flying cooking systems, control systems and associatedsensor(s) may be used to control the heat source(s) or burner(s) inoperation under certain conditions. For example, in a deep fryercontext, a control system and associated sensor(s) may be implemented toprevent a deep flyer from operating when a level of fluid, such ascooking oil or water for cleaning, is below a level needed toeffectively remove heat from the burners for heating the fluid forcooking or cleaning.

Known control systems may include sensors, such as level sensors, thatdirectly sense level of fluid based on position of a float on a shaft.In a cooking system context, the environment in which the sensor is usedmay not be conducive to smooth, continuous operation. For example, in adeep fryer context, debris may be present in the fluid in the system andcreate impediments to the float riding freely along the shaft. The floatmay become stuck at a level that does not indicate the actual level offluid. Sticking floats can create problems in such systems, such asproviding for operation of the burner/heater when insufficient fluid isin the system.

Capillary sensors are also known for fluid level sensing. Capillarysensors receive fluid into a capillary tube and determine level as afunction of the location of the fluid within the tube. In cookingenvironments, such as a deep flyer context to determine level of fluidin a fly vat, capillary sensors may be problematic due to differences inviscosity of the fluid that may need to be sensed. For example, somecooking fluids at certain temperatures will be in a partially solidphase so that capillary action within a capillary tube is not effectiveand level cannot be sensed (e.g. if the fluid is a solid at lowtemperatures such as is the case with lard).

Also, capillary sensors may retain fluid in the capillary creatingunsanitary conditions in use in a food-related context, because spaceswithin the capillary that retain fluid cannot easily be cleaned. Stillfurther, air pockets or bubbles that may be retained within thecapillary will be subject to temperature changes (sometimes extreme)that can cause sensor failure.

BRIEF SUMMARY

The present disclosure provides a sensor and control system thatoperates across a wide range of viscosities of fluid, from partiallysolid to low viscosity. The highly reliable and sanitary sensor isimplemented as a capacitive sensor that determines capacitance of thefluid that surrounds the sensor. In an illustrative embodiment thesensor according to the disclosure is disposed proximate to a groundedstructure of a container within which fluid is contained, e.g. proximateto the wall(s) of a vat or frypot in a deep fryer, wherein fluid in thevat may be fluid for cooking (e.g. cooking oil, lard or the like) orcleaning fluid (e.g. water or the like). The sensor is configured anddisposed to sense the capacitance of fluid in which the sensor islocated, e.g. between the sensor and wall of the vat or frypot, andthereby determine the relative capacitance of the fluid (and presence orabsence of same) in the vat.

The system according to the disclosure comprises the capacitive sensor,in communication with sensor electronics. The sensor electronicsinterface with a microcontroller or processor that is in communicationwith an interlock system for control of a subsystem. In the illustrativecooking vat context, the microcontroller is in communication with aheating system interlock that controls, e.g. enables or disables, aheating system such as one or more fuel burners used to heat the fluidin the vat (e.g. for cooking or cleaning).

In operation, in the illustrative embodiment, the capacitance of cookingoil (e.g. heated or around room temperature) is significantly differentthan the capacitance of air. The capacitance of air is alsosignificantly different than the capacitance of water. The controller,which receives a signal from the sensor electronics that isrepresentative of the measured capacitance from the sensor, candetermine the presence (and/or type) of fluid proximate to the sensorand thereby activate the interlock to either allow the heating system(e.g. burners) to operate, or prevent the heating system from operating.

In some embodiments, the sensor may be calibrated such that the sensedcapacitance (and therefore the existence and level of fluid proximate tothe sensor) is specifically based upon the position of the sensor withrespect to the walls and/or structures of the vat or frypot.

In an illustrative embodiment of a deep fryer, the fryer has a vatforming a frypot for receipt of a volume of oil. A sensor is disposedwithin the vat such that the sensor is disposed in contact with thevolume of oil within the frypot when oil is disposed within the frypot.The sensor is configured to detect the presence of oil within the frypotwhen a level of oil within the frypot is at or above the level of thesensor. The capacitive sensor is in communication with the controllerand sends a signal, via sensor electronics, to the controllerrepresentative of the presence or absence of oil within the frypot atthe level of the sensor. The controller interfaces to a heating systeminterlock and controls the condition of the interlock. The heatingsystem interlock, in turn, controls operation of one or more heatsources (e.g. burners) that extend through the vat. The condition orstate of the interlock enables or disables operation of the one or moreheat sources. The controller, based on the signal from the capacitivesensor via sensor electronics, puts the interlock in a state that allowsoperation of the heat sources when the signal received from the sensoris representative of fluid (e.g. oil for cooking or water for cleaning)being disposed within the frypot at or above the level of the sensor.The controller puts the interlock in a state that prevents operation ofthe one or more heat sources when the signal received from the sensorindicates that fluid is not disposed within the frypot at or above thelevel of the sensor.

Advantages of the present disclosure will become more apparent to thoseskilled in the art from the following description of detailedembodiments of the disclosure that have been shown and described by wayof illustration. As will be realized, the disclosed subject matter iscapable of other and different embodiments, and its details are capableof modification in various respects. Accordingly, the drawings anddescription are to be regarded as illustrative in nature and not asrestrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a capacitive sensor according to thedisclosure.

FIGS. 2A-2E are detailed views of components and assemblies of thecapacitive sensor of FIG. 1.

FIG. 3 is a functional block diagram of a control system utilizing thecapacitive sensor of FIG. 1.

FIG. 4 is a flow diagram of operation of the capacitive sensor of FIG. 1controlled by the control system of FIG. 3.

FIG. 5. is a perspective view of an illustrative embodiment of a deepfryer with a capacitive sensor according to the disclosure fordetermining the existence of oil within the frypot.

FIG. 6 is a detail view of FIG. 5.

FIG. 7 is a front cross-sectional view of the frypot of FIG. 5.

FIG. 8 is another front cross-sectional view of the frypot of FIG. 5.

FIG. 8a is a detail view of the view of FIG. 8.

FIG. 9 is a top view of a portion of the frypot, with the wire rackremoved for clarity.

DETAILED DESCRIPTION

A capacitive sensor probe constructed for installation in a fluidenvironment, according to the disclosure, is illustrated in FIG. 1. Thesensor probe 100 is configured and constructed to operate across a widerange of viscosities of fluid, from partially solid to low viscosity, ata wide range of temperatures, and is generally constructed of materialsthat are “food safe” as the materials may be used in a cookingenvironment in contact with foodstuffs. In operation, as described inmore detail hereinafter, the capacitive sensor probe acts as a “plate”of a capacitor, in conjunction with a metallic portion of theenvironment in which the probe 100 is housed (e.g. a portion of ametallic flyer vat) with the fluid disposed in the environment acting asa dielectric of the capacitor.

The sensor 100 is implemented as a capacitive sensor that senses thecapacitance of the fluid that surrounds the sensor. In an illustrativeembodiment the sensor according to the disclosure is disposed betweenthe walls of a vat, e.g. in a deep fryer, wherein fluid in the vat maybe fluid for cooking (e.g. cooking oil, lard or the like) or cleaningfluid (e.g. water or the like). The sensor is configured and disposed tosense the capacitance between the sensor and wall of the vat and therebydetermine the relative capacitance of the fluid (or lack of fluid) inthe vat, from which it can be determined that sufficient fluid ispresent in order to provide pertinent information to a control system.

A capacitive sensor probe according to the disclosure is bestillustrated in FIGS. 1, 2A-2E and 8A. The sensor 100 may include a metalcylindrical shell or probe radiator 102 that is disposed at an extremeend (e.g. the top) of the sensor assembly. The shell/radiator 102includes a recess 103 (best seen in FIG. 2B) that receives a receptacle104 press fit into the shell 102 for electrically conductive engagementwith the shell 102. The receptacle 104 is configured to receive astripped cable end 105 (Detail A of FIG. 2A) of a coaxial cable having acenter conductor, dielectric around the center conductor, and outerconductor, forming a coaxial electrode 106. The center conductor is inelectrical continuity with the radiator 102. The radiator 102 abuts aninsulator 107 that is configured to fit adjacent the radiator. In thisillustrative embodiment, the insulator 107 has threads that areconfigured to thread into the recess 103 of the radiator 102. An O-ring111 may be disposed between the radiator 102 and insulator 107. Theinsulator 107 may be made from PTFE, PEEK or other materials thatinsulate against electrical transmission and/or heat transmission andare also capable of withstanding temperatures such as up to about 500degrees Fahrenheit. A sensor mount 108 is disposed adjacent to and abutsthe insulator 107 and may have an O-ring disposed therebetween. Theinsulator 107 and sensor mount 108 are hollow so that the coaxialelectrode 106 can extend through those bodies. The coaxial electrode 106may be encased in PTFE heat shrink tube 109. A stripped cable end 110 ofthe coaxial electrode 106, distal from the radiator 102 is connected toa connector jack 113, with the outer conductor of the coaxial cable inelectrical continuity with a shell portion of the connector jack 113. Insome embodiments of the capacitive sensor 100, a fitting (not shown inFIGS. 1, 2A-2E and 8A) may be provided below the radiator 102 or belowthe insulator 107, to configure the sensor 100 to be attached to andremoved from a standpipe for inspection, cleaning, replacement or thelike.

As illustrated in FIG. 3, in the system according to the disclosure thecapacitive sensor probe 100 is in electrical/electronic communicationwith sensor electronics 140. The sensor electronics may comprisecapacitive sensor electronics in electrical communication with thesensor probe 100. In an illustrative embodiment the sensor electronics140 includes a Texas Instruments FDC1004 4-channelcapacitance-to-digital converter integrated circuit (IC), or substantialequivalent. A capacitive channel of the IC is electrically connected tothe inner conductor of the coaxial electrode 106 which is in turnconnected to the radiator 102 of the sensor probe 100. The IC andmetallic portion(s) of the tank are grounded to a common ground. Theouter conductor of the coaxial electrode 106 is electrically connectedwith the IC as an active or sensing shield to reduce electromagneticinterference and parasitic capacitance from sources other than thesensor probe 100. The sensor electronics 140 converts the analogcapacitive signal generated by the sensor electronics into a digitalsignal for communication, via a I²C serial bus, to a microcontroller orprocessor 142.

Referring still to FIG. 3, the microcontroller 142, for example a STM32family microcontroller available from STMicroelectronics, Geneva,Switzerland, receives the digital signal from the sensor electronics140. The digital signal is representative of a level of capacitancecreated by the fluid surrounding the sensor probe 100, and iscommunicated to the microcontroller 142 as a capacitive value. Themicrocontroller 142 is in communication with an interlock system (e.g. aheating interlock system) 144, which controls (enables/disables) aheating system 146 in communication with the interlock system 142.

Referring now to FIG. 4, illustrative processing by the microcontroller142 is illustrated. The microcontroller 142 reads the digital capacitivevalue 410 from the sensor electronics 140. The illustrative controlprocessing, implemented by microcontroller program code, then determinesif the capacitive value is within a minimum and maximum acceptable rangeof the sensor probe 100 and sensor electronics 140. An illustrativeacceptable range for a capacitance determination in a fryer vatapplication may be, for example 0 picofarad (pF) (minimum) to 16 pF(maximum). If the capacitive value is within the min/max range, then thecontroller may access a lookup table 414 and determine the appropriateoperation or control signal to output 416 to the interlock system (e.g.to enable or disable) the interlock 144 for control of the heatingsystem 146. In an illustrative implementation, the interlock system 144may include a solid state relay to enable or disable the heating system146.

Still referring to FIG. 4, if the capacitive value read by themicrocontroller 142 is not within the min/max range, and exceeds amaximum acceptable capacitive value (indicating a condition exists thatis outside the design specifications of the capacitive sensor probe 100and electronics 140), then the microcontroller issues a control signalthat may disable or reduce operation of the heating system or it maynotify an operator. In such a case, the microcontroller 142 may promptan operator for a decision to maintain or disable operation. In anembodiment, if the capacitive value read by the microcontroller 142 isnot within the min/max range, and exceeds a maximum acceptablecapacitive value (indicating a condition exists that is outside thedesign specifications of the capacitive sensor probe 100 and electronics140), then the microcontroller disables 418 the interlock 144 which inturn disables the heating system. A determination may be made todetermine if the capacitive value read by the microcontroller 142 is atan acceptable minimum capacitive value 420. The microcontroller 142 maybe programmed to determine if the capacitive value is at or near aminimum acceptable level, and if so to enable the interlock 144 but tocontrol the heating system with a heat limitation 422. Alternatively, ifthe capacitive value is not at or near a minimum acceptable level (e.g.is far below a minimum acceptable level) then the interlock 144 may bedisabled and the controller may issue an operator notification 424.

In an illustrative cooking context (e.g. where the capacitive sensor 100is disposed in a cooking vat or frypot as described in detailhereinafter), the microcontroller 142 is in communication with a heatingsystem interlock 144 that controls, e.g. enables or disables, a heatingsystem such as one or more fuel burners used to heat the fluid in acooking environment, for example where a fluid may be present forcooking or cleaning. As a function of the capacitive value received bythe microcontroller 142, the microcontroller sends a signal to theheating system interlock 144.

The sensed capacitance of cooking oil (e.g. heated or around roomtemperature) is significantly different than the capacitance of air. Thecapacitance of air is also significantly different than the capacitanceof water (or water with a cleaning solution or the like). The controller142, which receives the capacitive value signal from the sensorelectronics 140 that is representative of the measured capacitance fromthe sensor 100, can determine the presence (and in some configurationsthe type) of fluid proximate to the sensor and thereby activate theinterlock to either allow the heating system (e.g. burners) to operate,or prevent the heating system from operating.

Turning now to FIGS. 5-9, a deep fryer 10 embodiment is illustrated ingreater detail implementing the capacitive sensor 100 and control systemaccording to the disclosure. The deep fryer a vat 42 that receives andholds a volume of cooking oil or other cooking medium/liquid for cookingfood to be introduced into the deep flyer. A heat source 32 isconfigured to apply heat to the cooking oil disposed within the vat 42.The vat 42 is configured to receive one or more baskets (not shown) thathold food product to be cooked by contact or submersion in the heatedcooking liquid for a desired period of time.

The fryer 10 may be heated with the heat source 32, for example gasburners or electrical heating elements, to produce heat that istransferred to the cooking oil. In embodiments where gas burners areused, the burners may be positioned to ignite a flame outside of the vat42, with the combustion products sent through burner tubes 32 thatextend beneath the vat, with the surfaces of the burner tube 32transferring heat to the cooking liquid. In embodiments where electricalheaters are used, the heaters may be disposed directly within the vatsuch that the surface of the heaters contact cooking liquid for transferof heat to the cooking liquid.

Gas burners or electrical heaters both produce a large amount of heatduring operation to heat cooking liquid to cook food. In someembodiments where the cooking liquid is cooking oil, the heat sourcesoperate to heat the cooking oil within the vat to temperatures, forexample, in the range of 350 to 400 degrees Fahrenheit. In order for thebulk cooking oil temperature within the vat 42 to reach this temperaturerange, the heater sources need to be operate at higher temperatures thanthis range in order to transfer heat from the heat sources to thecooking oil. It is important during operation of burner systems andelectric heaters that the heat generated by these burners/heaters beremoved from the components during operation to prevent an excessivetemperature of the components, which can cause unsafe conditions such asfailure or damage to the components of the fryer or a fire hazard.Operation of the burners or heaters in the fryer 10 with minimal to nofluid, e.g. cooking oil or cleaning fluid, in the vat 42 causesundesirable heat build-up during operation. Accordingly, implementationof the capacitive sensor 100 and control system as described hereinprevents heating sources from operating when the vat 42 does not includesufficient fluid to remove heat. However, it should be appreciated thatthe capacitive sensor and control system described herein may beimplemented in other contexts where an interlock (e.g. enable/disablemechanism) may be used and a capacitive value of a fluid within areceptacle can be used to control the interlock (for example, any ofvarious systems with a fluid reservoir and delivery control components,or the like). It should be noted that the same operation as describedwill apply in other contexts as well, such as when cleaning fluid ispresent, or not, in the vat for purposes of operation to clean the vat.

As illustrated, e.g. in FIG. 5, the flyer 10 with burner interlockincludes a vat 42. The vat includes a front wall 26, opposite right andleft side walls 22, 24, and a rear wall 28. Burner tubes 32 extendthrough a bottom portion of the vat 42, typically through the front andback walls 26, 28. A grate 40 may be provided above the burner tubes 32,with the grate 40 providing a surface that a flyer basket (not shown butconventional) can rest upon when food within basket is being friedwithin the cooking oil, and specifically heated cooking oil that isdisposed above the burner tubes 32.

The capacitive sensor 100, as described hereinbefore in relation toFIGS. 1, 2A-2E, and 3, is disposed within the vat 42 in a position withthe radiator (102, best shown in FIG. 1) at a level representative ofthe desired minimum cooking oil level within the vat for needed heatremoval from the burner tubes 32 for safe operation. The sensor 100 isprovided to detect the presence of cooking oil at a necessary level forsafe operation, and to provide a signal to a microcontroller 142 (FIG.3). The sensor, via the sensor electronics 140 (described hereinbefore),provides the controller 142 with a capacitive value signal that isrepresentative of the presence or absence of cooking oil proximate tothe sensor at the necessary level within the vat 42. The microcontroller142 receives the capacitive value signal and based upon the signalreceived either provides control signals to the heating system interlock144 to allow operation of the burners (when the signal indicates thatcooking oil is present at the necessary level) or prevents operation ofthe burners (when the signal indicates that cooking oil is not presentat the necessary level).

An example location of the capacitive sensor according to the disclosureis illustrated in FIGS. 6 through 9. As illustrated in FIG. 7, in thecontext of a cooking oil vat, a portion of the sensor 100 may rest on astandtube 120 that extends within the vat. The standtube 120 is of aheight that places the radiator 102 of the sensor 100 at a heightoptimized for the proper fluid level. The coaxial communications cable106 extends through the standtube 120 and is connected to the sensorelectronics (140, FIG. 3) which is in turn electrically connected to themicrocontroller 142. The capacitive sensor 100 produces a capacitivevalue as a function of the fluid that surrounds the sensor, i.e. betweenthe sensor and the walls of the vat (in the location depicted in thefigures the front 26 and adjacent wall 22 of the vat 46), with thesensor probe acting as one plate of a capacitor and the wall(s) of thevat acting as a second plate of the capacitor. The capacitance ofcooking oil (heated or around room temperature) is significantlydifferent than the capacitance of air, such that the microcontroller142, receives a capacitive value signal that is representative of themeasured capacitance of the fluid present. Based on the capacitivevalue, the microcontroller 142 sends control signals to the heatingsystem interlock 144 to either allow the burners to operate, or preventthe burners from operating. It should be appreciated that withappropriate programming, the microcontroller 142 may determine what typeof fluid is proximate to the sensor or may determine the presence ofdebris or other material within the fluid.

In some embodiments, the sensor 100 may be calibrated such that thesensed capacitance (and therefore the existence and level of fluidproximate to the sensor) is specifically based upon positioning of thesensor 100 within the vat. That is, sensed capacitive value may be afunction of the position of the sensor with respect to, for example, awalls of the vat (22, 26), or in another example the side wall of aburner tube 32. While the system may be calibrated based upon thespecific position of the sensor within the vat, in relation to astructure of the vat, one of ordinary skill in the art should appreciatethat calibration may be based on non-vat structures placed in proximityto the sensor and made a part of the circuit/system as described herein.Generally, sufficient space should exist between the sensor and thestructure (e.g. wall) for an amount of fluid to be positioned betweenthe sensor and structure for a reliable and repeatable capacitance levelof fluid, e.g. cooking oil, to be achieved.

As described, the microcontroller receives a signal from the sensor 100,via the sensor electronics 140, that is proportional to the capacitanceof fluid present, which capacitance may be calibrated based on the typeof fluid. Memory in association with the microcontroller (e.g. a look-uptable) maintains capacitance information based upon type of fluid, e.g.appropriate ranges or “windows” of capacitive value, that are correlatedto control signals to send to the system interlock 144, to either allowor prevent burner operation. based upon the determined type of fluid.

In a specific illustrative embodiment, the sensor may be positioned asdepicted in FIGS. 8, 8A and 9, with the sensor 100 disposed within aspace 99 within the vat 42 that is proximate to the side wall 32 b ofthe burner tube, and the front and right walls 26, 22 of the vat 42.This positioning allows for the sensor 100 to interact with the cookingoil (or lack thereof) within the vat 42, yet be protected by the wallsof the vat and the side of the burner tube to minimize damage during useof the fryer 10. As illustrated, the sensor may be positioned with itscenter 112 substantially evenly spaced between the right side wall 22and the adjacent burner tube 32, as depicted with the space X. In thisexample, the center 112 of the sensor 100 is disposed approximately 0.9inches from the right side wall 22 and approximately 0.9 inches from theburner tube 32 (distance Z). The outer circumference of the sensor 100,and specifically the radiator 102) in this illustrative embodiment isapproximately 0.75 inches, establishing a space of approximately 0.52inches between the outer wall of the radiator 102 and the right wall 22and as well as the burner tube 32. In this embodiment, the center 112 ofthe sensor is positioned approximately 0.6 inches from the front wall 26of the vat 42 (Y), as well as approximately 0.6 inches from a wall 29that is substantially parallel to the front wall 26 and forms the sideof an inward indentation 22 b of the right side wall 22 (W) as discussedbelow. With an amount of cooking oil disposed in the space between theradiator 102 and the various walls of the vat 42 and side wall of theburner tube 32, a capacitance value of a particular fluid within thespace (i.e. cooking oil) is significantly different than a sensedcapacitance of air disposed in the space between the radiator and thewalls of the vat 42. Similarly, the sensed capacitive value of thatfluid (e.g. cooking oil) is significantly different than a sensedcapacitance of water that might otherwise be disposed in the space (e.g.for a cleaning operation).

As shown in FIGS. 8 and 8A, in this example embodiment the sensor 100 ispositioned vertically with respect to the top surface 32 a of the burnertube 32 that is proximate to the sensor 100. The top of the sensor maybe aligned to be just below the top surface 32 a of the burner tube asdepicted by distance T. The distance T may be approximately 0.25 inches.In other embodiments, the top of the sensor 100 may be at the sameheight as the top surface 32 a of the burner tube 32 (i.e. the distanceT is 0 inches). In such an embodiment, the sensor 100 may be no higherthan the top surface 32 a of the burner tubes 32 to avoid the sensorinteracting with a frybasket disposed within the vat 42 (which normallyrests upon the wire rack 40, best seen in FIGS. 5 and 6).

The vertical position of the sensor 100 within the vat 42 may generallybe aligned with the top surface 32 a of the burner tube 32 such that thepresence or absence of oil, based upon the capacitance measured by thesensor 100, is representative of the level of oil that would be neededto cover the burner tubes in order to sufficiently remove heat away fromthe burner tube 32 and transfer that heat to the cooking oil within thevat 42.

In some embodiments, the sensor 100 and system may be calibrated toprovide a signal that is understood by the controller that cooking oilsurrounds the sensor 100 when the sensor 100 is fully covered by cookingoil (in some embodiments, specifically the radiator shell 102), i.e.cooking oil surrounds the entire circumferential side surface of thesensor 100. In some embodiments, the sensor 100 and system may becalibrated to provide a signal that is understood by the controller thatcooking oil surrounds the sensor 100 when about 90% of the verticalheight, or in other embodiments 90% of the total circumferential area,of the sensor 100 is surrounded by cooking oil. Other calibrations maybe contemplated and within the scope of the disclosure.

While the embodiments depicted in FIGS. 8, 8A and 9 and discussed hereininclude a sensor disposed in particular position within the vat, itshould be appreciated by those skilled in the art that the sensor may belocated or otherwise disposed at other locations in the vat.

In some embodiments, the controller may be programmed to provide anerror message to the user (by way of a message board, digital readout,warning light, or the like when the measured capacitance does not fallwithin a value (or range of values) of calibrated capacitance of cookingoil (room temperature through hot), water, or air. In this case, it ispossible that the sensor 100 is not operating properly, or it ispossible that the surfaces of the sensor 100 or perhaps the surfaces ofthe walls that are proximate to the sensor 100 (side wall 22, burnertube 32, or the like) are covered with foreign materials such that themeasured capacitance differs from the normally calibrated capacitance.The error message may prompt the user to investigate the cause, and totake steps to cure same, e.g. mechanically cleaning the surface of thesensor 100 or the walls of the vat 42 to try to clear the error message.

As shown in FIGS. 7-9, in some embodiments, the right and left sidewalls 22, 24 may be configured to maximize the amount of oil that isdisposed within the vat 42 above the burner tubes and minimize theamount of oil that is within the vat on the sides of the burner tubes32. This construction improves the circulation of oil within the vat andminimizes the localized heating of oil for a longer oil life. In someembodiments, the right and left side walls may include a narrowed region22 b (left side 24 wall has the same design as the right wall 22) wherethe portion of the right wall 22 b that is aligned with the sides of theburner tubes 32 extends inwardly to minimize the space between the rightwall and the side of the burner tube 32, while allowing the volume ofthe vat above the burner tubes to be wider above the burner tubes.

Although the sensor as described herein is configured and disposed tosense the capacitance between the sensor and wall of the vat in theillustrative embodiment, and thereby determine the relative capacitanceof the fluid (or lack of fluid) in the vat, from which it can bedetermined that sufficient fluid is present in order to providepertinent information to a control system, it should be appreciated bythose skilled in the art that rather than a metallic/conductive wall ofthe vat the sensor may be used as described to determine capacitancebetween the sensor and another structure, and the capacitive sensor andcontrol system according to the disclosure may be used in a differentcontext other than a frying vat. For example, in a non-flyer context (ornon-metallic or metallic reservoir context), a conductive structure maybe provided (rather than a wall of the context structure) proximate tothe sensor, and operate in accordance with the disclosure to sensecapacitance of the content of the reservoir.

While the interlock system and heating system are described andillustrated herein as discrete systems, it should be appreciated thatthe interlock mechanism controlling the controlled system (e.g. heatingsystem), as a result of the capacitive value, may be an integratedsystem with the interlock mechanism as an integrated part of thecontrolled, e.g. heating/burner, system.

While various embodiments are disclosed herein, it should be understoodthat the invention is not so limited and modifications may be madewithout departing from the disclosure. The scope of the disclosure isdefined by the appended claims, and all devices that come within themeaning of the claims, either literally or by equivalence, are intendedto be embraced therein.

What is claimed is:
 1. A capacitive sensor probe, comprising: a metalshell radiator disposed at an extreme end of a sensor assembly; acoaxial electrode electrically interconnected to the metal shellradiator, the coaxial electrode having a center conductor, a dielectricaround the center conductor, and an outer conductor, the centerconductor being in electrical continuity with the metal shell radiator;an insulator configured to fit adjacent the metal shell radiator, andconfigured to electrically and thermally isolate the metal shellradiator from selected electrical and thermal properties in anenvironment wherein the capacitive sensor probe is disposed; and aconnector disposed distal from the metal shell radiator on the coaxialelectrode, a portion of the connector being in electrical continuitywith the metal shell radiator via the outer conductor of the coaxialelectrode and a second portion of the connector being in electricalcontinuity with the metal shell radiator via the center conductor of thecoaxial electrode.
 2. The capacitive sensor probe of claim 1, furtherincluding a sensor mount disposed adjacent to the insulator, theinsulator and sensor mount having interior hollow portions with thecoaxial electrode extending through the interior hollow portions.
 3. Thecapacitive sensor probe of claim 1, wherein the metal shell radiator iscylindrical.
 4. The capacitive sensor probe of claim 1, wherein themetal shell radiator includes a recess that is configured to receive areceptacle press fit into the metal shell radiator to provide forelectrically conductive engagement of other components of the capacitivesensor probe with the metal shell radiator.
 5. The capacitive sensorprobe of claim 1, wherein the coaxial electrode is a coaxial cable. 6.The capacitive sensor probe of claim 5, wherein a portion of the coaxialcable forming the coaxial electrode is press fit into a receptacle pressfit in the metal shell radiator to provide for electrically conductiveengagement of the portion of the coaxial electrode of the capacitivesensor probe with the metal shell radiator.
 7. The capacitive sensorprobe of claim 1, wherein the insulator has threads that are configuredto thread into a portion of the metal shell radiator.
 8. The capacitivesensor probe of claim 1, wherein the insulator is constructed from amaterial that insulates against at least one of electrical transmissionor heat transmission up to approximately 500 degrees Fahrenheit.
 9. Thecapacitive sensor probe of claim 1, wherein the capacitive sensor probeis configured to be disposed within a deep fryer vat such that thecapacitive sensor probe is disposed to communicate with a volume offluid within the deep fryer vat.
 10. The capacitive sensor probe ofclaim 9, wherein the capacitive sensor probe is in electricalcommunication with a control system and the sensor and control systemare calibrated for determining presence of fluid in the vat.
 11. Thecapacitive sensor probe of claim 9, wherein the capacitive sensor probeis positioned proximate to an inner metallic corner of the deep fryervat sensing capacitance of a volume of fluid within the deep fryer vatbetween the capacitive sensor probe and the inner metallic corner of thedeep fryer vat.
 12. A capacitive sensor and system, comprising: acapacitive sensor disposed within a vat and positioned to communicatewith a volume of fluid within the vat, the capacitive sensor having ametal radiator disposed at an extreme end of a sensor assembly, acoaxial electrode electrically interconnected to the metal radiator, thecoaxial electrode having a center conductor, a dielectric around thecenter conductor, and an outer conductor, the center conductor being inelectrical continuity with the metal radiator, an insulator configuredto fit adjacent the metal radiator, and configured to electrically andthermally isolate the metal radiator from selected electrical andthermal properties, and a connector disposed distal from the metalradiator on the coaxial electrode, a portion of the connector being inelectrical continuity with the metal radiator via the outer conductor ofthe coaxial electrode and a second portion of the connector being inelectrical continuity with the metal radiator via the center conductorof the coaxial electrode; sensor electronics processing a signal inelectronic communication with the capacitive sensor; and a controllerreceiving the signal from the sensor electronics representing acapacitive value from the capacitive sensor and transmitting controlsignals to control operation of one or more devices based on thecapacitive value.
 13. The capacitive sensor and system of claim 12,wherein the controller allows operation of the one or more devices whenthe signal received from the capacitive sensor is representative offluid being disposed within the vat at or above a level of thecapacitive sensor.
 14. The capacitive sensor and system of claim 12,wherein the controller prevents operation of the one or more deviceswhen the signal received from the capacitive sensor is representative offluid not being disposed within the vat at or above a level of thecapacitive sensor.
 15. The capacitive sensor and system of claim 12,wherein the capacitive sensor is positioned proximate to an innermetallic corner of the deep fryer vat sensing capacitance of a volume offluid within the deep fryer vat between the capacitive sensor and theinner metallic corner of the deep fryer vat.
 16. The capacitive sensorand system of claim 12, wherein the insulator is constructed from amaterial that insulates against at least one of electrical transmissionor heat transmission up to approximately 500 degrees Fahrenheit.
 17. Amethod of constructing a capacitive sensor, comprising: providing ametal radiator disposed at an extreme end of a sensor assembly;configuring a coaxial electrode electrically interconnected to the metalradiator, the coaxial electrode having a center conductor, a dielectricaround the center conductor, and an outer conductor, the centerconductor being in electrical continuity with the metal radiator;positioning an insulator configured to fit adjacent the metal radiator,and configured to electrically and thermally isolate the metal radiatorfrom selected electrical and thermal properties in an environmentwherein the capacitive sensor probe is disposed; and connecting aconnector disposed distal from the metal radiator on the coaxialelectrode with a portion of the connector being in electrical continuitywith the metal radiator via one of the outer conductor of the coaxialelectrode and the center conductor of the coaxial electrode.
 18. Themethod of constructing a capacitive sensor probe further including asensor mount disposed adjacent to the insulator, the insulator andsensor mount having interior hollow portions with the coaxial electrodeextending through the interior hollow portions.
 19. The method ofconstructing a capacitive sensor probe of claim 17, wherein the step ofproviding a metal radiator disposed at an extreme end of a sensorassembly involves providing a cylindrical metal radiator.
 20. The methodof constructing a capacitive sensor probe of claim 17, wherein the stepof configuring a coaxial electrode electrically interconnected to themetal radiator involves electrically connecting a portion of coaxialcable to the metal radiator.